PROCESS FOR DEPOLYMERIZING TEREPHTHALIC POLYESTERS INTO DIETHYL TEREPHTHALATE DIESTER AT ROOM TEMPERATURE

Abstract

The present invention relates to the field of recycling materials containing polyester terephthalate, particularly polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or polytrimethylene terephthalate (PTT), commonly used in the manufacture of disposable plastic bottles, food trays, textiles, and composite insulation materials. It specifically concerns a process for recycling PET into terephthalic diester, and in particular dimethyl terephthalate (DMT), in less than one hour and without any pretreatment steps. Furthermore, this process uses products with a low environmental impact. It is therefore particularly advantageous from an industrial perspective.

Description

Title of the invention: PROCESS FOR DEPOLYMERIZING TEREPHTHALIC POLYESTERS INTO TEREPHTHALATE DIESTER DIETHYLATE AT ROOM TEMPERATURE

[0001] The present invention relates to the field of recycling materials containing polyester terephthalate, in particular polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), commonly used in the manufacture of disposable plastic bottles, food trays, textiles, composite insulation materials, etc. It relates specifically to a process for recycling PET into diethyl terephthalate (DET) diester in less than one hour and without any pretreatment steps. Furthermore, this process does not use products with a lower environmental impact than those used in prior art processes. It is therefore particularly advantageous from an industrial perspective.

[0002] Scope of the invention

[0003] PET recycling is an important environmental issue and thus represents a commercial opportunity due to its widespread use, abundance, and durability. However, recycling PET-based materials is complex and varies depending on the type of polymer, the material design, and the type of finished product.

[0004]

[0005] The main obstacle to the use of recycled plastics is the contamination of waste streams with different types of polymers that are incompatible with each other. Consequently, it is often not possible to add recycled PET plastic to virgin polymer without diminishing certain quality attributes, such as color, clarity, or impact resistance. Therefore, the ability to replace virgin polymer with recycled PET depends heavily on the purity of the recycled product and the requirements of the final product.

[0006]

[0007] According to the principle of chemical recycling, PET can be depolymerized by solvolysis such as methanolysis or glycolysis, or by hydrolysis, and the monomers thus obtained can be reused to generate new PET polymers called "recycled PET".

[0008] DET obtained by ethanolysis is a monomer of interest because it is easier to dissolve than DMT, produced by methanolysis. The latter requires the use of larger volumes of solvent to keep it dissolved. and thus be able to perform purification operations such as filtration and decolorization. Furthermore, the resulting DET can be oxidized and then used to produce terephthalic acid. As an example, document WO2007 / 076384 describes an ethanolyse reaction of PET in which PET, or a terpolymer comprising a terephthalate monomer and ethylene glycol monomers, is reacted with ethanol. This reaction produces ethylene glycol and an aromatic diethyl ester, such as diethyl isophthalate and / or diethyl terephthalate. The recovered diethyl components can be subjected to liquid-phase oxidation to produce aromatic carboxylic acid.

[0009] Most PET depolymerization processes begin with a chemical pretreatment step aimed at swelling the material to be treated or a mechanical pretreatment to amorphize the material to be treated.

[0010] It is desirable to have improved, low-cost and easily industrially operable PET-based material recycling processes in order to facilitate the generalization of this recycling and to broaden the fields of use of recycled PET, and more generally of polyester terephthalate. Description of the invention

[0011] The inventors have developed a new, particularly efficient depolymerization process by mild ethanolysis for recycling materials containing polyester terephthalate, in particular polyethylene terephthalate (PET), polybutylene terephthalate (PBT), or polytrimethylene terephthalate (PTT), into diethyl terephthalate diester (DET). This process is very rapid while being much more environmentally friendly than prior art processes. It provides access to DET in solid form, which, due to its purity, is directly reusable in crystalline form.

[0012] Thus, the invention relates to a process for recycling a material comprising a terephthalate polyester into a diethyl terephthalate diester comprising two steps:

[0013] a. a step of grinding or shredding said material to produce fragments, and

[0014] b. a step of depolymerizing the terephthalate polyester into diethyl terephthalate diester, in the presence of:

[0015] (i) of a catalyst: a metallic or organic ethoxide base

[0016] (ii) of a polar ester-type solvent of formula A

[0017] (iii) of an alcohol: ethanol

[0018] characterized in that: - said base is present in a catalytic quantity relative to the quantity of PET - said depolymerization step is carried out at room temperature or by heating up to 80°C for a period of between 1 minute and 4 hours.

[0019] The polyester terephthalate-based material may be a plastic, a textile or another type of material containing 100% polyester terephthalate (PET, PBT or PTT) or a composite material containing a mixture of PET and / or PBT and / or PTT with other constituents such as cotton, polyamide, polyurethanes, polyolefins and fluorinated polymers, such as a composite plastic, a multifiber textile or an insulating composite material, cellulosic fibers (viscose, lyocell, natural fibers such as flax...). Advantages of the invention

[0020] A first significant advantage: this process does not require pretreatment, a step that necessitates the use of toxic products. The depolymerization reaction is sufficiently efficient to allow complete depolymerization without pretreatment (chemical or thermomechanical) of the material to be treated. Thus, the process according to the invention is simpler (one less step), more environmentally friendly, faster, less expensive, and requires little energy input. The ability to reduce the amount of solvents needed for the reaction and for maintaining the monomers in solution allows for substantial energy savings during the evaporation step for solvent recycling.

[0021] Since the process presents a very moderate industrial risk, the industrial facilities for its implementation can therefore be set up more easily, as the level of safety requirements for these facilities is less stringent. Regulatory compliance is simplified during plant installation and throughout the production cycle. Capital expenditure (CAPEX) is thus significantly reduced.

[0022] The solvent used for depolymerization is an ester. This type of solvent is less toxic than the products used in the prior art; these are products that are notably used in the food industry, in the field of flavorings.

[0023] Remarkably, the depolymerization reaction is very rapid and complete. This is applicable to PET as well as PBT or any other type of terephthalate-patterned polyester, such as PTT, which are thus depolymerized into DET. These are then recyclable and have recognized industrial applications and a market.

[0024] The process can be described as "very rapid" since the reaction is complete in less than 4 hours at room temperature, and in less than 20 minutes under optimized heating conditions, particularly between 60 and 80°C. It starts instantly and can lead to complete depolymerization in as little as 1 minute.

[0025] The depolymerization reaction is simple. After completion of the reaction, fibrous or coated materials that are not PET-based are easily pre-filtered. The resulting reaction medium contains DET in solution. DET is thus isolated after crystallization. Washing the solid DET removes intermediate or degradation products to separate them from the product of interest, whereas laborious distillation operations are required to achieve this separation in state-of-the-art depolymerization processes.

[0026] This process can be applied to any type of material comprising a terephthalate polyester, in particular PET, PBT or PTT, pure or mixed, transparent or colored, regardless of its thickness or composition.

[0027] Decolorization is easy and very effective on activated carbon or other absorbent support such as silica, ion exchange resins, clay... It allows obtaining a very clear, even transparent, reaction medium.

[0028] Those skilled in the art know that composite and multifiber textile materials can be manufactured in various ways. They can be woven and coated in several layers, or be non-woven. They are composed of different materials, in particular polyester blended with other materials.

[0029] The nature of the "polyester" type materials may differ and, by way of non-exhaustive list, may include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polylactic acid (PLA), polycaprolactone (PCL), polyester furanoate (PEF)...

[0030] Other materials blended with polyester may include, but are not limited to, polyamide (Nylon 6,6 or hexamethyldiamine diadipate, Nylon 6 or polycaprolactam, etc.), polyurethanes, natural fibers with a cellulosic pattern such as cotton; artificial cotton derivatives such as viscose, Lyocell, Tencell, etc.; polyolefins (polypropylene, polyethylene), and fluoropolymers (the latter are generally coated). Fluoropolymers are used for their waterproofing and insulating properties; for example, polytetrafluoroethylene (PTFE). Among polyurethanes, elastane is particularly valued because it provides flexibility to the textile and breathable properties, especially when it is a flexible elastomeric polyurethane, the two main commercial forms of which are poly(ether)urethanes and poly(ester)urethanes.

[0031] The use of polyamides in varying proportions with PET has many applications in the clothing sector (lingerie and sportswear) but also in technical textiles for their highly absorbent and dust-free properties (microfiber wipes for industrial wiping). However, it is not currently possible to recycle a composite material including elastane, polyamides or coated materials, which is problematic in terms of waste management; the process according to the invention provides a solution to this problem.

[0032] Furthermore, the process according to the invention is particularly advantageous for recycling polyester terephthalate-based composite materials because the reaction is selective with respect to polyester terephthalate and does not dissolve other materials. This allows for the easy separation of depolymerized polyester terephthalate in the form of DET monomers from the other components.

[0033] Another differentiating advantage of the process is that it allows the recovery of materials separated from polyester terephthalate after its depolymerization, in an unaltered form. Polyamide (polyamide 6; polyamide 6,6), elastane, and cotton are concrete examples in the textile industry. The process described in this patent makes it possible to isolate the components initially mixed with polyester terephthalate with a degree of purity that allows for their subsequent recycling. It should be noted that one of the highly innovative applications of this process is to enable the recovery of elastane or polyamide from polyester terephthalate-based composite materials and their reuse in new applications.

[0034] The process yield is high: at least 85%, particularly for the depolymerization of PET into DET. Furthermore, the material mixed with polyester is fully recovered.

[0035] For the depolymerization of PET to DET by ethanolysis using the ester solvent combined with ethanol and a metal or organic ethoxide (second-order solvent and base), the product obtained is 99.9% pure at the end of the reaction. Given its level of purity, it can be used in numerous applications, for the regeneration of DMT or other diesters; PET; or any other type of engineering resin involving this monomer. The choice of reagents and the implementation of mild conditions ensure that no isomerization reaction occurs, nor the formation of degradation products that impair the quality of the product obtained. When present, these reaction secondary molecules disrupt the polymerization reaction, and purification of the recycled raw DET is therefore necessary before its use.

[0036] This process is more economical and environmentally friendly than existing processes because the bases (catalysts) are used in smaller, or even significantly reduced, quantities compared to the amount of polyester terephthalate to be recycled, and because the reaction temperatures are below 100°C, generally between ambient temperature (around 25°C) and 80°C, and the reaction times are much shorter than those of PET depolymerization processes described in the literature. Furthermore, ethanol is an alcohol with very low toxicity (unlike methanol commonly used for PET depolymerization).

[0037] In particular, ethanol is used in proportions ranging from 0.25 to 14 molar equivalents relative to polyester terephthalate; preferably from 1.1 to 5 molar equivalents relative to polyester terephthalate, which is a substantial improvement compared to conventional methanolysis technologies in which proportions of 25 molar equivalents are required, but also compared to methanolysis processes described to date.

[0038] The proportions of the polar ester-type solvent are also reduced, with a minimum ratio of 1:1.5 with respect to the mass of polyester terephthalate:volume of the solvent mixture. Preferably, this ratio is at least 1:3, or even 1:4, or even 1:5, and even more preferably 1:6.

[0039] From an ecological point of view, it should be noted that the depolymerization bath containing the solvent can be reused for a new treatment cycle once the product has been filtered. The bath can be used at least twice without affecting the efficiency of the reaction. Once the reaction is complete, the solvents can be recovered by simple, energy-efficient distillation, given their low boiling point. DETAILED DESCRIPTION OF THE INVENTION

[0040] The invention relates to a process for recycling a material comprising a polyester terephthalate, pure or in mixture, into a terephthalate diester comprising two steps:

[0041] a. a step of grinding or shredding the waste to produce fragments, and

[0042] b. a step of depolymerizing said polyester into terephthalate diester in the presence of:

[0043] (i) of a catalyst selected from a metallic or organic ethoxide base

[0044] (ii) of a polar solvent which is an ester of formula A

[0045] [Chem.l] (HAS)

[0046] in which R is chosen from an aryl CnH2n, alkyl CnH2n+1 or CnH2n1 with n = 1 to 10

[0047] (iii) of an alcohol is ethanol

[0048] characterized in that: - said base is present in a catalytic quantity relative to the quantity of said polyester in a mass ratio of at least 5% - said depolymerization step is carried out at room temperature or by heating up to 80°C for a period of between 1 minute and 4 hours.

[0049] This process is applicable to the recycling of all types of terephthalic patterned polyester, the most commonly used of which are PET and PBT.

[0050] Materials comprising polyester terephthalate may be composed of 100% polyester terephthalate (for example plastics or textiles) or be composed of a mixture comprising polyester terephthalate and other components such as cotton, cellulosic fibers (viscose, lyocell, natural fibers such as flax,...), polyamide, elastane, PTFE, polyethylene, polypropylene (for example composite plastics, multifiber textiles or composite insulation panels).

[0051] When the material comprising polyester terephthalate is made up of 100% polyester terephthalate, this material is transformed into terephthalate diester.

[0052] The terephthalate polyester is preferably chosen from polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), which are commonly used polymers. However, it may be any other type of terephthalate-patterned polyester such as triethylene terephthalate (PTT), polylactic acid (PLA), polycaprolactone (PCL), polyethylene furanoate (PEF)...

[0053] In a particular embodiment of the invention, the material is composed of 100% polyester terephthalate selected from polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate.

[0054] When the material comprising polyester terephthalate is a composite material comprising polyester terephthalate mixed with other components, the recycling process 1) produces terephthalate esters (DET) by depolymerizing the polyester terephthalate, 2) recovers the other components of the material in an unaltered solid form in the reaction mixture. These other components, being in solid form, can be separated from the DET in solution by filtration. The recovery of these components allows for their reuse; some of these "recycled" components constitute a raw material sought after by industry.

[0055] The composite material comprises polyester terephthalate selected from polyethylene terephthalate and polybutylene terephthalate, mixed with another constituent selected from cotton, cellulosic fibers (viscose, lyocell, natural fibers such as flax...) polyamide, polyurethanes, polyolefins and fluorinated polymers.

[0056] In another particular embodiment of the invention, the material is a composite material comprising terephthalate polyester selected from the polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate mixed with another constituent selected from cotton, polyamide, polyurethanes, polyolefins and fluorinated polymers.

[0057] In a more particular embodiment, polyurethane is elastane.

[0058] Thus, in a particular embodiment in which the material comprising PET is a composite material comprising PET mixed with other components, the recycling process allows the transformation (recycling) of PET into DET and the release of the other components (which can also be recycled).

[0059] The invention therefore also relates to a recycling process for a composite material comprising a polyester terephthalate blend with other components as defined above, wherein the component(s) recovered after depolymerization for reuse are selected from polyethylene terephthalate, polybutylene terephthalate, cotton, cellulosic fibers (viscose, lyocell, natural fibers such as flax, etc.), polyamide, polyurethanes, in particular elastane, polyolefins, and fluorinated polymers. Indeed, it is possible to recover the component(s) of interest, which may be a polyester or another component.

[0060] Thus, the process according to the invention provides alternatively, for example, a process for recycling elastane from a composite material comprising elastane mixed with PET.

[0061] The catalyst is an ethoxide base selected from, for example, lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, barium ethoxide, titanium ethoxide.

[0062] The catalyst is present in a molar ratio of less than 35% relative to the terephthalate polyester, preferably between 0.5 and 20%.

[0063] The ester-type solvent preferably corresponds to formula A:

[0064] [Chem.l] (HAS)

[0065] in which R is chosen from an aryl CnH2n,alkyl CnH2n+1 or CnH2n 4 with n = 1 to 10

[0066] In a preferred embodiment, the polar solvent is ethyl acetate, a solvent of low toxicity.

[0067] In a preferred embodiment of the invention, the mass ratio of polyester terephthalate to solvent volume is between 1:1.5 and 1:10. In a way Preferably, this ratio is at least 1:3, or even 1:4, or even 1:5 and even more preferably 1:6.

[0068] The alcohol used during the depolymerization step is ethanol.

[0069] The amount of ethanol involved in the depolymerization reaction is variable. The alcohol can either be supplied by the base in solution (in an alcohol), or added directly to the reaction medium. The ethanol can thus be in excess, in an equivalent amount, or in deficiency relative to the amount of polyester terephthalate. This parameter will be adjusted by a person skilled in the art.

[0070] Ethanol is present in a ratio of between 0.25 and 16 molar equivalents relative to polyester terephthalate. In another preferred embodiment of the invention, the ethanol:polyester terephthalate molar ratio is between 0.5 and 14; preferably between 0.6 and 9; more preferably precisely between 1.1 and 5.

[0071] Advantageously, the process is carried out by applying a mass ratio of polyester terephthalate to volume of solvent of between 1:1.5 and 1:10, preferably between 1:1.5 and 1:6 and a molar ratio of ethanol to polyester terephthalate of between 0.25 and 10. In a particular embodiment, the process is carried out by applying a mass ratio of polyester terephthalate to volume of solvent of between 1:1.5 and 1:6 and a molar (equivalent) ratio of ethanol to polyester terephthalate of between 0.25 and 6.

[0072] A particular feature of the invention is the use of an alcohol, an ester, and a base of the same order, namely order 2, in the depolymerization reaction. This combination has the advantage of enabling a complete depolymerization reaction, which is particularly efficient and allows for the production of pure products. The terephthalate monomers are thus solubilized in DET. Cooling the solution is sufficient to precipitate them and recover a purified solid product.

[0073] If the material comprises a mixture of polyester terephthalate and other non-polyester based components, the latter will not be modified, will remain in suspension and will be easily removed by filtration.

[0074] In a preferred embodiment of the invention, the depolymerization of the terephthalate polyester is obtained in the presence of ethanol, ethyl acetate and sodium ethoxide.

[0075] The base involved in the depolymerization reaction is in catalytic quantity relative to the quantity of polyester terephthalate to be treated.

[0076] The term "catalytic quantity" refers to a non-stoichiometric amount of base, i.e., in a molar ratio of 1% to 49% relative to the amount of polyester terephthalate to be treated. The term "catalytic" also applies to a reactant that is recovered in its initial form at the end of the reaction (catalyst).

[0077] In a preferred embodiment of the invention, said base is present in a catalytic quantity in a ratio of 5 to 12% by mass relative to the amount of said polyester, preferably in a ratio of 6 to 9% by mass, and more preferably 6 to 8% by mass relative to the amount of said polyester. Extended reaction times can be applied to further reduce this quantity, thereby reducing the cost of the reaction.

[0078] The reaction temperature can vary. The reaction medium can be heated up to 80°C. The mixture can advantageously be heated between 60°C and 80°C, preferably below 70°C, i.e., between 60 and 70°C. Heating reduces the reaction time. However, it is very interesting to note that the reaction proceeds very well at room temperature (around 25°C) while also being rapid, as complete depolymerization is achieved in 3 to 4 hours. Not heating the reaction simplifies implementation and reduces cost.

[0079] The present invention will be better understood upon reading the following examples, which are provided by way of illustration and shall in no way be considered as limiting the scope of the present invention. EXPERIMENTAL SECTION

[0080] EXAMPLE 1: Depolymerization of 100% PET by ethanolys

[0081] A quantity (500 g) of PET pieces from different sources (Textiles, food trays, water bottles, etc.) are introduced into a solution containing 2 L of ethyl acetate and 99 mL of a sodium ethoxide solution (21% in ethanol), corresponding to a molar ratio of 15% sodium ethoxide (which corresponds to sodium ethoxide) to PET. The reaction starts instantly. After 45 minutes of reaction at 70°C, all the PET fragments have disappeared, leaving behind a homogeneous reaction mixture, colored in the case of textiles. The crude reaction mixture is filtered using a Buchner funnel to retain the unreacted material. The recovered mixture contains DET, monoethylene glycol (a product of the depolymerization reaction), the base initially used in the reaction, and the solvent mixture. After decolorization using activated carbon, the DET (423 g) is recovered as a pasty solid following evaporation of the solvents and cooling of the reaction mixture.Finally, the residue is washed with ethanol. The reaction yield is 73%.

[0082] EXAMPLE 2: Depolymerization of PET-based textiles by ethanolys

[0083] A quantity (500 g) of PET / Elastane 69 / 31% textile pieces is introduced into a solution containing 2.4 L of ethyl acetate, 600 mL of ethanol, and 131 mL of a sodium ethoxide solution (21% in ethanol) corresponding to a molar ratio of 20% sodium ethoxide to the PET present. The reaction starts instantly. After 60 minutes of reaction at 70°C, the All of the PET disappeared, leaving behind undegraded elastane fragments. The crude reaction mixture was filtered using a Buchner funnel to retain 154 g of unreacted material. This material was then washed and dried. The recovered filtrate contained DET, monoethylene glycol (a product of the depolymerization reaction), the base initially used in the reaction, and the solvent mixture. After decolorization using activated carbon, the DET (359 g) was recovered as a pasty solid following solvent evaporation and cooling of the reaction mixture. Finally, this solid was washed with ethanol. The reaction yield was 73% relative to the initial amount of PET in the textile.

Claims

Demands

1. A process for recycling a material comprising polyester terephthalate, pure or in mixture, into terephthalate diester comprising two steps: a. a step of grinding or shredding said material to produce fragments, and b. a depolymerization step of said polyester into terephthalate ester in the presence of: (i) a catalyst selected from a metal or organic ethoxide base (ii) a polar solvent of the ester type of formula A: (A) O in which R is selected from an aryl CnH2n,alkyl CnH2n+1 or CnH2n i with n = 1 to 10 (iii) an alcohol: ethanol characterized in that: - said base is present in catalytic quantity relative to the quantity of said polyester in a mass ratio of at least 5% - said depolymerization step is carried out at room temperature or by heating up to 80°C for a duration of between 1 minute and 4 hours.

2. A method according to claim 1 wherein said material is composed of 100% polyester terephthalate selected from polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate.

3. A method according to claim 1 wherein said material is a composite material comprising polyester terephthalate selected from polyethylene terephthalate, polybutylene terephthalate and polytrimethylene terephthalate mixed with another constituent selected from cotton, polyamide, polyurethanes, polyolefins and fluorinated polymers.

4. Method according to claim 3 wherein said polyurethane is elastane.

5. A process according to any one of claims 1 to 4 wherein said catalyst is an ethoxide selected from lithium ethoxide, sodium ethoxide, potassium ethoxide, magnesium ethoxide, barium ethoxide, titanium ethoxide.

6. A process according to any one of claims 1 to 5 wherein said catalyst is sodium ethoxide or potassium ethoxide.

7. A method according to any one of claims 1 to 6 wherein said catalyst is present in a molar ratio of between 0.5 and 20% relative to the terephthalate polyester.

8. A method according to any one of the preceding claims wherein said polar ester-type solvent corresponds to formula A is ethyl acetate.

9. A process according to any one of the preceding claims wherein the mass ratio of polyester terephthalate to volume of solvent is between 1:1.5 and 1:

10.

10. A method according to any one of the preceding claims wherein the (equivalent) molar ratio alcohol: terephthalate polyester is between 0.25 and 6.

11. A recycling process according to claim 3 wherein the material recovered after depolymerization for reuse is selected from polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, cotton, polyamide, polyurethanes, in particular elastane, polyolefins and fluorinated polymers.